Liquid Crystal Display (LCD) is the most widely used one among various types of flat-panel display devices at present. The main component part of a LCD is a liquid crystal panel which mainly comprises a color film substrate, an array substrate and liquid crystal provided therebetween. Thin Film Transistors (TFTs) are disposed in the array substrate. Electric fields are generated by pixel electrodes connected with the TFTs, so as to control the driving of the liquid crystal and realize image display.
In a liquid crystal panel, in order to obtain uniform arrangement and initial directions of liquid crystal molecules, it is required to align the liquid crystal. In prior arts, the initial directions of liquid crystal molecules are generally controlled by means of an alignment film. The alignment film is disposed at one side of each of the color film substrate and the array substrate facing the liquid crystal layer, and is endowed with an alignment capability by a rubbing process. In the rubbing process, a rubbing roller whose outer surface is coated with rubbing cloth is generally used to roll on the alignment film in a set direction. By means of the rubbing force applied to the alignment film by the cloth, alignment grooves with consistent directions are formed on the surface of the alignment film, such that the liquid crystal molecules are arranged along the alignment grooves in a certain direction to realize the alignment of the liquid crystal.
In the rubbing process, the rubbing roller also applies a pressure in the vertical direction to the alignment film. As a consequence, the flatness degree of the rubbed side of the alignment film has a great influence on the depth of the alignment groove. If there exists a height difference somewhere on the rubbed side, the fibers of the rubbing cloth will create uneven deformations such that alignment grooves with uneven depths are formed on the rubbed side. However, for a liquid crystal panel, a display area for image display and a non-display area surrounding the periphery of the display area generally have different flatness degrees. In general case, in each of the color film substrate and the array substrate, the region corresponding to the display area is relatively flat. However, in the non-display area shown in FIG. 1, especially in the region 4 of the array substrate corresponding to the non-display area, because there exists, in the signal unit 1 on the array substrate, wiring 11 and 13 between the TFTs and the driver chip, segment differences due to fabrication process which have a plurality of different heights are formed between the signal unit 1 and the gap region 2 in the non-display area. Meanwhile, in order to ensure the product yield, as shown in FIG. 1, a test pad 31 is generally further disposed in the non-display area, and the structure of the test pad 31 is only partially the same as that of the TFT. Meanwhile, a corresponding test via-hole 32 may be further disposed in the test pad 31 as required. A drive signal is loaded through the test via-hole 32 and transmitted via wiring 33 so as to test the TFT array after some key process. In the case where the test via-hole 32 is disposed in the test pad 31, a big segment difference is formed between the test via-hole 32 and respective functional layers in the array substrate.
When rubbing alignment is performed on the array substrate by using the rubbing process, the rubbing cloth will create different deformations due to the influence from the big segment difference on the substrate surface. Because the deformations of the cloth fibers have a certain cumulative property (or memory property), if the fiber deformations due to the segment difference are not relieved in time, then on one hand, the utilization rate and service life of the cloth will be decreased dramatically, causing the degree of badness of the rubbed side to increase gradually, and on the other hand, such deformations will lead to uneven rubbing strength of the cloth on the substrate, thereby causing uneven depths of the alignment grooves formed in the alignment film. The uneven depths of the alignment grooves tend to cause the badness such as Rubbing Mura to occur along the rubbing direction, thereby decreasing the product yield.
The Rubbing Mura is a serious quality problem in the rubbing process. It not only seriously influences the image quality of a product, but also has a low ET detection rate, which leads to a serious waste of resource and material at the back end as well as quality problem. Meanwhile, as to what kind of wiring structure can be used in the color film substrate and the array substrate (especially the array substrate) to reduce the Rubbing Mura, it is a difficult problem in the rubbing process all the time.